Chapter 3

 symbolic representation of a chemical reaction that shows: ◦ reactants on left side of reaction ◦ products on right side of equation ◦ relative amounts of each with stoichiometric coefficients ◦ attempt to show on paper what is happening at the molecular level

 Matter is not created or destroyed, there is no detectable change in quantity of matter in an ordinary chemical reaction  discovered by Lavoisier  balance chemical reactions using coefficients  balancing equations is a skill acquired only with lots of practice  propane,C 3 H 8, burns in oxygen to give carbon dioxide and water C 3 H O 2  3 CO H 2 O there are equal numbers of atoms of each element on both sides of equation

 Ex. 1) How many CO molecules are required to react with 27 formula units of Fe 2 O 3 to make iron and carbon dioxide  Ex. 2) What mass of CO is required to react with g of iron (III) oxide?  Ex. 3) How many pounds of carbon monoxide would react with 128 pounds of iron (III) oxide?

 Most experiments do not have the exact amounts needed to completely react. LR helps us decide which reactant is in excess (the one we have plenty of) and which reactant is limiting (the one that will determine the outcome of the reaction)  ~ If a box has 87 bolts, 113 washers and 99 nuts, how many sets consisting of one bolt, two washers and one nut can you make?  Ex. 4) What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g of carbon disulfide with 111 g of oxygen? (combustion rxn)

 Most rxns in real life do not go to completion. A few reasons why ◦ Reactants did not react 100% to give the products ◦ Side reactions can occur to form undesirable products as well as the wanted products  theoretical yield is what we have been calculating on paper  actual yield is what you have made in the lab

 Ex 5) A 10.0 g sample of ethanol, C 2 H 5 OH, was boiled with excess acetic acid, CH 3 COOH, to produce 15.0 g of ethyl acetate, CH 3 COOC 2 H 5. What is the percent yield? (The other product is H 2 O)  Ex 6) Using the percent yield from Ex. 5, how much C 2 H 5 OH, is needed to give a yield of 45.0 g of CH 3 COOC 2 H 5 ?

 Sequential ~ multiple steps are needed for a rxn to go to completion  Ex. 7) Starting with 100. g of benzene (C 6 H 6 ), calculate the theoretical yield of nitrobenzene (C 6 H 5 NO 2 ) and of aniline (C 6 H 5 NH 2 ). (1 to 1 mole ratios)  Ex. 8) If 46.7 g of aniline is prepared from 100. g of benzene, what is the percentage yield?

 solution – a homogeneous mixture of 2 or more substances. Usually one substance is dissolved in another  solute – what gets dissolved  solvent – what does the dissolving (water is the universal solvent)  concentration - amount of solute dissolved in a solvent  Mass of solution = mass of solute + mass of solvent  % by mass of solute = mass of solute x 100% mass of solution

 Ex. 9) Calculate the mass of potassium nitrate required to make 277 g of solution that is 20.0% KNO 3 by mass. What is the mass of water in the solution?  Ex. 10) What volume of 24.5% lead(II) nitrate solutions contains 40.0g of lead(II) nitrate? The density of the solution is 1.25 g/mL

 molarity = mol solute/L of solution = M  Ex. 11) Calculate the molarity of a solution that contains 12.8 g of sulfuric acid in 1.70 L of solution.  Ex. 12) Determine the mass of calcium nitrate required to prepare 3.55 L of M solution.  Ex. 13) The specific gravity of concentrated HCl is and it is 36.31% w/w HCl. What is its molarity?

 number of moles of solute remains constant  M 1 V 1 = M 2 V 2 works because # of moles is constant  If 10.0 mL of 12 M HCl is added to enough water to give 100. mL of solution, what is concentration of the new solution?  Ex. 14) What volume of 18.0 M sulfuric acid is required to make 2.50 L of a 2.44 M sulfuric acid solution?

 Combine the ideas of molarity and stoichiometry  Ex. 15) What volume of M BaCl 2 is required to completely react with 4.32 g of Na 2 SO 4 ?  Ex. 16) a) What volume of M NaOH will react with 50.0 mL 0f M aluminum nitrate? b) What mass of aluminum hydroxide precipitates?

 method of determining the concentration of solutions once the concentration of a standard solution is known  requires special glassware - buret, pipet, flasks, and an indicator  Ex. 17) What is the molarity of a barium hydroxide solution if 44.4 mL of M HCl is required to react with 38.8 mL of the barium hydroxide solution?

 In the lab, acid-base rxns are carried out as a titration: ◦ Standard solution: a soln of known concentration ◦ Standardization: process by which the conc. of a standard soln is determined. ◦ Equivalence point: point in a titration at which chemically equivalent amounts of reactants have reacted ◦ Endpoint: point in a titration where the indicator changes color and the titration is stopped.